Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. Once a wellbore has been drilled, the well must be completed before hydrocarbons can be produced from the well. A completion involves the design, selection, and installation of equipment and materials in or around the wellbore for conveying, pumping, or controlling the production or injection of fluids. After the well has been completed, production testing of the well can begin.
Hydrocarbon wells for the exploitation of oil and/or gas from a reservoir normally consist of an upper and outer conductor, which forms the base of the well, an upper casing arranged into and in extension of the conductor, and further down in the well more casings which are arranged into and overlaps the above casing. A production tubing string is located in the middle of the well for transporting petroleum from the bottom of the well to the earth s surface or to the sea floor. Annuli will then be formed between the different casings.
As the production from a well gradually falls, all wells will sooner or later have to be abandoned. Before the well is permanently abandoned, the well must be securely plugged, where there are official requirements with respect to how the work is to be carried out and to its completion. For this purpose, normally cement plugs are used to provide a barrier in the well.
First decision is if the production tubing string in the middle of the well must be pulled. This is a requirement if cables are un on its outside. Without cables, production tubing could be left to save operational time. This will then add one extra annulus.
A common requirement during plug-and-abandonment operations is to have a plug set inside an inner casing string and a further plug set in the annulus between the inner casing string and the outer casing string (or borehole formation). The plug will then extend across the full cross sectional area of the well.
Normally, one of the following methods and technologies are used to install a cross sectional cement barrier and thus plug and abandon hydrocarbon wells: (1) Section casing milling; (2) Squeezing cement by use of perforation and cement retainer; and (3) the Perforation, Washing, and Cementing (PWC) technique.
The section casing milling is common practice, running a mill (similar to bit) in the borehole on a drill string (drill-pipe) and milling the casing at the desired well depth. While milling, drilling fluid is pumped down and circulating to clean the well from the metal debris. Several trips are needed to replace a worn mill with the new mill to mill out a required interval (ca. 100 m for a combined plug). Large volume of swarf (debris or waste resulting from the milling) is produced, and handling the swarf is a complex procedure. After milling operation is completed, part of the hole section will become fully exposed to the formation rock (open-hole). An under-reamer is run to enlarge the open hole and clean the well prior to cementing. The required cement volume is pumped down through a drill-string and placed in the open-hole section. The cement is then tested and verified as a rock-to-rock barrier.
Disadvantages of the section casing milling method include:                Time consuming, many rig days (ca. 21-30 days for a 100 m plug);        Risk of swarf and debris handling;        Potential for swarf damaging the blow-out preventer (BOP);        Risk of pipe getting stuck due to poor hole cleaning (because of swarf);        Several trips are required to change the mill.        
With the technique in which cement is squeezed by use of perforation and a cement retainer, the casing can be perforated conventionally in two different depths, e.g. approximately 100 m apart. Normally, one perforation is provided and circulation will normally go through the entire annulus to the surface. The cement retainer is a special plug which is used to squeeze cement through it, and hold pressure to prevent back-flow of cement (“U-tube effect”) after cement has been injected. The cement retainer is run separately, via wireline, coiled tubing or drill-string. In general, a cement retainer is an isolation tool set in the casing or liner that enables treatments to be applied to a lower interval while providing isolation from the annulus above. Cement retainers are typically used in cement squeeze or similar remedial treatments. A specially profiled probe, known as a stinger, is attached to the bottom of the tubing string to engage in the retainer during operation. When the stinger is removed, the valve assembly isolates the wellbore below the cement retainer.
Disadvantages with this technique include:                It is difficult to verify new annulus cement as the perforation is plugged by cement which remains below the cement retainer;        Multiple trips required.        
The so-called PWC technique may be done in one trip. It consist of perforating the section with guns; washing the perforated section; then placing the cement plug. To avoid some of the disadvantages listed below, drilling the perforation could be an option, but then more time consuming.
Disadvantages associated with the co-called PWC technology include:                May damage the casing;        Unable to perform cement bond log (CBL);        Unable to verify new annulus cement barrier;        Extended operation time; multiple trips required (typically four trips for a 100 m plug);        Use of explosives;        Extreme caution may be necessary (nearby producer wells may have to be shut off).        
The known methods of performing annular sealing during temporary or permanent plugging of hydrocarbon wells are all having the goal of placing cement in the annulus in a secure and safe manner via either holes in the tubular or by directly pumping in the annulus: a) so-called shoot and squeeze, which displaces the fluid by use of an open-ended drill pipe or tubing, b) top down cementing, c) circulation squeeze, d) hesitation squeeze. All of the above methods a)-d) have challenges relating to conforming the cement over the full interval, this relates both to the placing as well as the logging. The placing of the cement is not conclusive as the cement will have to change place with the annulus fluids present in the annulus prior to placing barrier cement. The fluid which is present in the annulus needs to be evacuated/forced to either above or below the interval or through the formation rock by formation leak-off.
The current logging technologies. e.g. Ultra-Sonic Imager Tool (US IT). Cement Bond Log (CBL). Segmented Bond Tool (SBT), have proven very subjective regarding being to able to conclusively confirming or verifying that the barrier is sealing properly in the annulus. The current designs of today's logging tools are fully dependent on a logging-friendly downhole environment, i.e. the environment needs to fulfill certain demands to be able to perform a proper logging operation.
The prior art includes WO 2012/096580 A1, which describes a method and washing tool for combined cleaning of an annulus in a well across a longitudinal section of the well, and subsequent plugging of the longitudinal section.
US 20150053405 describes a method where the cement is placed into the tubular whereafter the cement is pressurized out of the tubular and into the annulus.
U.S. Pat. No. 2,072,982 describes a method where the cement charge is subjected to the action of a mechanical vibrator while driving the cement into an annulus through perforations in the casing.
U.S. Pat. Nos. 5,152,342 and 3,335,801 describe methods where devices are located on the casing string. Some of the cement will flow through a bypass section to power the devices and cause vibrations in the casing steel. As with vibrations in the cement, the objective is to gain better cement bonding. Being mechanical devices, the techniques are limited in frequency selection and bandwidth.
It is therefore a need for a plugging tool and method that can simplify the plugging process.